This invention relates to phenazine dyes, and more particularly, to phenazine dyes suitable as intermediates for leuco phenazine dyes.
Phenazine dyes have been used for many industrial purposes for over 100 years. Well known examples of phenazine dyes include Heliotrope B, and phenosafranine. Essentially all of the phenazine dyes capable of providing red, orange, and magenta hues have unsubstituted amine groups at the 3- or 7-position, or both.
The presence of unsubstituted amine groups at the 3- or 7-positions, or both, does not allow one to employ a simple, direct method to reduce and acylate the dye at the 10-position without also acylating the dye at the 3- or 7-position or both. In a reduced leuco dye which contains acyl groups at the 10-position as well as the 3- and/or 7-positions, reoxidation under normal conditions removes only the acyl group at the 10-position, which will yield a dye form having different absorption properties from that of the original, unreduced dye containing the unsubstituted amine group. Therefore, phenazine dyes known in the art, such as phenosafranine, which are red, magenta, and the like, do not provide the original dye color upon reduction, acylation and reoxidation. In addition, a phenazine dye acylated at the 10-position and containing a free amine group at the 3 and/or 7-positions provides a very unstable leuco dye form in an imaging system containing a metal nitrate, due to the presence of the unsubstituted amine group. Thus, there is no known method for providing phenazine dyes which can be converted to stable leuco forms and then reoxidized to give orange, red and magenta colors in a metal nitrate system. Although phenazine dyes containing substituents at the 3- and 7-positions are well known, essentially all of them provide turquoise or blue colors.
British Patent Specifications 1,443,403 and 1,440,948 describe phenazine dyes for use on cellulosic and other fibers having substituents on the 3- and 7-positions. These substituents are sulfonated phenyl and sulfonated benzyl groups. Although these sulfonated groups provide enhanced water solubility of the dye, they cannot be converted to stable leuco forms that can be oxidized to form orange, red, or magenta colors. British Patent Specification 1,193,923 describes phenazine dyes having long chain alkyl groups attached to the aromatic rings thereof. Although long alkyl chains reduce the mobility of and diffusibility of the dyes, they impart a high molecular weight and low solubility, and they cannot be converted to stable leuco forms that can be oxidized to form orange, red, or magenta colors.